Complete determination of the material composition of municipal solid waste incineration bottom ash.

Bottom ash from waste incineration is heterogeneous and contains different materials. Previous studies on the material composition of bottom ash provide only limited information as to composition, because large pieces present in bottom ash were not investigated nor were all materials were separated and analysed. The objective of the present study is to provide the complete and detailed composition of bottom ash encompassing and extensive range of different materials. Altogether, nine bottom ash samples with a mass of 3000 kg each were sieved to eight size fractions, whereby small particles adhering to larger pieces were separated by water and added to the respective size fractions. In the sorting analysis of all size fractions, the materials enclosed in molten mineral material and materials present as composites (e.g. transformers and batteries) were considered. The material characterisation revealed that the size fraction > 50 mm contains most of the iron (up to 50% of the total iron) and copper (about 20% of the total copper), while batteries, coins, silver and gold are almost exclusively present between 16 and 50 mm. The fractions between 8 and 16 mm show the highest share of aluminium (up to 50% of the total aluminium) and glass (up to 60% of the total glass). While the metal content is underestimated, if large pieces of material are disregarded, the multi-step approach applied in this study enables a complete determination of materials in bottom ash, which is essential for optimising material recovery in bottom ash treatment.

Chemical composition and leachability of differently sized material fractions of municipal solid waste incineration bottom ash.

The chemical composition and leachability of municipal solid waste incineration bottom ash are important parameters determining its suitability for utilisation. The objective of the present study is to investigate the chemical composition of individual size and material fractions and their contribution to the total elemental contents of bottom ash. Nine bottom ash samples with a mass of 3000 kg each were sieved to eight size fractions and sorted into different materials. The materials (mineral material, glass, batteries) were separately analysed by inductively coupled plasma optical emission spectrometry after acid digestion. Additionally, x-ray fluorescence measurements and leaching tests were performed. Metals were further analysed by sorting analysis. The chemical analysis revealed that large particles have higher contents of Fe and Si, but lower contents of Ca and S compared to smaller particles. All mineral fractions exceed the legal limit values for utilisation in Austria mainly because of the total contents of Pb and Tl and the leachate contents of Cr and Sb. Glass from bottom ash is enriched in As, Na, Si and Tl compared to the mineral material. Although battery contents contribute only 0.2% to the total mass of bottom ash, they contribute at least 30% to the total content of Cd. Most previous studies neglected large metallic pieces and batteries, which contain most of the Cd, Cr, Cu and Ni present in bottom ash. This practice can result in an underestimation of the total contents of these elements by up to about 70%.

Sample preparation and determination of biomass content in solid recovered fuels: a comparison of methods.

The biomass content of material from pulp and paper production (a mixture of waste and paper and thin layer packaging plastics) is determined by the adapted balance method. This novel approach is a combination of combustion elemental analysis (CHNSO) and a data reconciliation algorithm based on successive linearisation for evaluation of the analysis results. It also involves less effort and expense than conventional procedures. However, the CHNSO technique only handles small mass amounts (few hundred milligrams), so cryogenic impact milling was applied for particle size reduction below 200 µm in order to generate homogeneous, representative analysis samples. The investigation focuses on the parameters biogenic content as a percentage of the total mass xB and xB (TC), which is the biomass stated as a fraction of the total carbon value. The results are within 1%-5% of the data obtained by the reference methods, namely the selective dissolution method and (14)C- method. Additionally, advantages and drawbacks of the adapted balance method in comparison with standard methods are discussed, showing that the adapted balance method is a method to be considered for the determination of biomass content in solid recovered fuels or similar materials.

Sample preparation and biomass determination of SRF model mixture using cryogenic milling and the adapted balance method.

The biogenic fraction of a simple solid recovered fuel (SRF) mixture (80 wt% printer paper/20 wt% high density polyethylene) is analyzed with the in-house developed adapted balance method (aBM). This fairly new approach is a combination of combustion elemental analysis (CHNS) and a data reconciliation algorithm based on successive linearisation for evaluation of the analysis results. This method shows a great potential as an alternative way to determine the biomass content in SRF. However, the employed analytical technique (CHNS elemental analysis) restricts the probed sample mass to low amounts in the range of a few hundred milligrams. This requires sample comminution to small grain sizes (<200 µm) to generate representative SRF specimen. This is not easily accomplished for certain material mixtures (e.g. SRF with rubber content) by conventional means of sample size reduction. This paper presents a proof of principle investigation of the sample preparation and analysis of an SRF model mixture with the use of cryogenic impact milling (final sample comminution) and the adapted balance method (determination of biomass content). The so derived sample preparation methodology (cutting mills and cryogenic impact milling) shows a better performance in accuracy and precision for the determination of the biomass content than one solely based on cutting mills. The results for the determination of the biogenic fraction are within 1-5% of the data obtained by the reference methods, selective dissolution method (SDM) and (14)C-method ((14)C-M).

Analysis of total copper, cadmium and lead in refuse-derived fuels (RDF): study on analytical errors using synthetic samples.

Components with extraordinarily high analyte contents, for example copper metal from wires or plastics stabilized with heavy metal compounds, are presumed to be a crucial source of errors in refuse-derived fuel (RDF) analysis. In order to study the error generation of those 'analyte carrier components', synthetic samples spiked with defined amounts of carrier materials were mixed, milled in a high speed rotor mill to particle sizes <1 mm, <0.5 mm and <0.2 mm, respectively, and analyzed repeatedly. Copper (Cu) metal and brass were used as Cu carriers, three kinds of polyvinylchloride (PVC) materials as lead (Pb) and cadmium (Cd) carriers, and paper and polyethylene as bulk components. In most cases, samples <0.2 mm delivered good recovery rates (rec), and low or moderate relative standard deviations (rsd), i.e. metallic Cu 87-91% rec, 14-35% rsd, Cd from flexible PVC yellow 90-92% rec, 8-10% rsd and Pb from rigid PVC 92-96% rec, 3-4% rsd. Cu from brass was overestimated (138-150% rec, 13-42% rsd), Cd from flexible PVC grey underestimated (72-75% rec, 4-7% rsd) in <0.2 mm samples. Samples <0.5 mm and <1 mm spiked with Cu or brass produced errors of up to 220% rsd (<0.5 mm) and 370% rsd (<1 mm). In the case of Pb from rigid PVC, poor recoveries (54-75%) were observed in spite of moderate variations (rsd 11-29%). In conclusion, time-consuming milling to <0.2 mm can reduce variation to acceptable levels, even given the presence of analyte carrier materials. Yet, the sources of systematic errors observed (likely segregation effects) remain uncertain.

Sewage sludge ash to phosphate fertilizer by chlorination and thermal treatment: residence time requirements for heavy metal removal.

Heavy metal removal from sewage sludge ash can be performed by mixing the ash with environmentally compatible chlorides (e.g. CaCl2 or MgCl2) and water, pelletizing the mixture and treating the pellets in a rotary reactor at about 1000 degrees C. Thermogravimetry-mass spectroscopy, muffle oven tests (500-1150 degrees C) and investigations in a laboratory-scale rotary reactor (950-1050 degrees C, residence time 1-25 min) were carried out. In the rotary reactor, up to 97% of Cu, 95% Pb and 95% Zn can be removed at 1050 degrees C. As Cl release starts from 400 degrees C (obtained from thermogravimetry-mass spectrometry experiments), heavy metals are already removed partially within the heating period. This heavy metal removal can be described as being similar to a first-order rate law. To meet the limit values specified in the Austrian and German fertilizer ordinances, residence times of the order of minutes are sufficient at 950 degrees C.

Limitations for heavy metal release during thermo-chemical treatment of sewage sludge ash.

Phosphate recycling from sewage sludge can be achieved by heavy metal removal from sewage sludge ash (SSA) producing a fertilizer product: mixing SSA with chloride and treating this mixture (eventually after granulation) in a rotary kiln at 1000 ± 100°C leads to the formation of volatile heavy metal compounds that evaporate and to P-phases with high bio-availability. Due to economical and ecological reasons, it is necessary to reduce the energy consumption of this technology. Generally, fluidized bed reactors are characterized by high heat and mass transfer and thus promise the saving of energy. Therefore, a rotary reactor and a fluidized bed reactor (both laboratory-scale and operated in batch mode) are used for the treatment of granulates containing SSA and CaCl(2). Treatment temperature, residence time and - in case of the fluidized bed reactor - superficial velocity are varied between 800 and 900°C, 10 and 30 min and 3.4 and 4.6 ms(-1). Cd and Pb can be removed well (>95 %) in all experiments. Cu removal ranges from 25% to 84%, for Zn 75-90% are realized. The amount of heavy metals removed increases with increasing temperature and residence time which is most pronounced for Cu. In the pellet, three major reactions occur: formation of HCl and Cl(2) from CaCl(2); diffusion and reaction of these gases with heavy metal compounds; side reactions from heavy metal compounds with matrix material. Although, heat and mass transfer are higher in the fluidized bed reactor, Pb and Zn removal is slightly better in the rotary reactor. This is due the accelerated migration of formed HCl and Cl(2) out of the pellets into the reactor atmosphere. Cu is apparently limited by the diffusion of its chloride thus the removal is higher in the fluidized bed unit.